Add source distribution to PyPI deployment.

Author: t-sommer

.travis.yml

@@ -59,5 +59,5 @@ deploy:
   user: t-sommer
   password:
     secure: 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
-  distributions: bdist_wheel --universal
+  distributions: sdist bdist_wheel --universal
   skip_cleanup: true